My defining moment - the one that made me decide I am an artist - was
brought
on by a grade-school art teacher too, though it's not the way the rest of
you would
have expected... :)

In the fifth grade I was late cleaning up my area before leaving the art
room.
I overheard my teacher ask a couple of girls if they would like to
participate in
a state art competition (Olympics of the Visual Arts hosted in Albany, NY).
I came up to him and asked why he didn't think to ask if I would like to
enter.
He said that boys don't have stick-to-it-iveness or some such drivel, which
immediately made me decide, "Well, I'll show him!" I entered, took 2nd
(lost
to a class of students working on the same project - they really should do
something to make that competition more equal), but it was enough to make
me believe in myself. From then on I stopped listening when anyone told
me I couldn't do something.